The prior art for child resistant bottle closures generally includes three types of "safety cap." A first type has a ratchet locking system between closure and bottle in which the ratchet locking is permanent. It can be released only by fracturing an intentionally weakened portion of the system. This alternative is intended for tamper evidence, and is not useful for bottles which must maintain child resistance after multiple reclosings.
A second type of child resistant bottle closure has a resilient closure which is manually deformable to disengage a ratchet locking system between bottle and closure. This alternative is child resistant for multiple reclosings. However, squeezing a closure, which must have significant stiffness to serve its primary function as a closure, is often difficult for adults with arthritis.
A third type of child resistant bottle closure has a rigid closure and requires manual deformation of a resilient bottle feature. "Safety caps" of the third type are child resistant for multiple reclosings, and they are typically more adult friendly because the child resistant feature does not have to serve another purpose. Because the rigid closure of the third type "safety cap" cannot be inadvertently deformed, and because a child normally grips and manipulates the closure portion of a bottle in an attempt to enter it, the third type of "safety cap" generally provides the greatest child resistance. Instead of deforming the closure, the third type of "safety cap" has specific locations adjacent to the closure must be pressed to release the closure. The third type of "safety cap" is the type to which the present invention pertains.
Within the third type of child resistant closure there exists in the art a number of alternative constructions. One construction includes a collar attached to a bottle, wherein the collar has two 180.degree. opposing, radially depressed pushtabs that are cantilevered from the bottoms of the pushtabs. When each pushtab is pressed near its center, a locking surface at the outer end of the pushtab releases a mating closure surface.
The term "radially depressed" herein means that pushtabs are pressed inward toward each other predominantly along a radius of the bottle finish. Radial depression is the optimum choice wherever two pushtabs must be depressed by one hand. They are usually depressed by a thumb and forefinger. Radial depression of opposing pushtabs ensures that both pushtabs have to be depressed simultaneously. Otherwise individually depressed pushtabs will return to their locking position when released.
Another construction has two 180.degree. opposing pushtabs that are cantilevered from the sides of the pushtabs. Pushtabs rotate inward along a curved path which is approximately radial. Similar to the pushtabs cantilevered from their bottoms, pressing occurs at the center of the pushtab and the release of locking surfaces occurs at the outer end of the pushtabs.
A significant disadvantage of prior art pushtab designs is their poor leverage. That is, pressing at a point between the pushtab cantilever and the closure locking surface requires higher pushtab pressing forces than if pressing occurred outwardly of the closure locking surface. It has been found that in order to achieve child resistance, pushtabs must have either relatively short strokes and high depression forces or relatively long strokes and low depression forces. However, relatively high pushtab depression forces are also difficult for adults to manage. An adult user-friendly pushtab depression force should be less than about 2 lbs. It is therefore advantageous to provide pushtabs with longer strokes and lower forces. For a given pushtab depression force and stroke, it is also beneficial to have leverage between the pushtab force and the closure releasing force so that the closure releasing force can be high enough that the closure cannot be released by over twisting it against the locking mechanism.
It is believed that child resistance is also enhanced by making pushtabs unobvious for a child to press. Pushtabs which extend beyond the outermost surface of the closure are more obvious for a child to press than flush mounted or recessed pushtabs. Flush or recessed pushtabs guarded by a rigid surface adjacent to the edges of the pushtabs is another feature believed to enhance child resistance by minimizing inadvertent depressions.